This project is a study of the effects of oral L-arginine on the vasodilatory capacity of skeletal muscle vasculature in patients with coronary atherosclerosis, heart transplantation, and normal vascular endothelium. Our goal is to demonstrate whether oral L-arginine can enhance hyperemic blood flow as measured by venous occlusion plethysmography. The time course, dose, and pharmacokinetic properties of oral L-arginine will also be studied.